When blood is collected from a predetermined position of a body for the purpose of various tests, it sometimes happens that such position is injured by a member having a sharp front end portion so as to exudate the blood from that position. A device called a lancet is used for such injuring. For example, in order to measure a glucose concentration in blood, a fingertip, an ear lobe or a palm is injured so as to collect blood.
The lancet used for the blood collection generally comprises a lancet cap and a lancet body, which are formed integrally by means of a weakened portion between them, so that a pricking member (such as a needle) extends through that portion while straddling them.
Upon blood collecting, a rear end portion of the lancet body is inserted into an injector which ejects the lancet toward a predetermined position, so that the lancet is loaded on the injector. Then, the weakened portion is broken so as to remove the lancet cap from the lancet body, so that an front end portion of the pricking member is exposed from a front end portion of the lancet body. When such lancet body is ejected thereafter, such exposed front end portion instantaneously moves toward and sticks the predetermined position, that it pricks the predetermined position, and then returns back immediately.
Pricking as mentioned above is an operation to injure a body by means of a sharp member. Before carrying out pricking, people whose blood is collected have a kind of tension in that they would feel some pain, and just upon pricking, they feel some pain. It is desirable that such tension and pain are depressurized as much as possible. For such depressurizing, it is conceived that a finer needle is used as the pricking member. The finer needle is desirable from a viewpoint of depressurizing, but there comes up a problem in that such needle is readily bent due to its less rigidity.
The lancet as mentioned above is produced by an injection molding process wherein a molten resin is injected into a mold in which a pricking member is inserted beforehand followed by solidifying the injected resin. When the pricking member is finer, a force generated by means of inertia of the injected molten resin is applied to the pricking member supported in the mold, so that molding may be carried out while the pricking member is in its curved (or flexed) state. For example, it is possible that a front end portion of the pricking member is curved (or flexed).
In the case wherein the front end portion of the pricking member is curved (or flexed), it is possible that said portion is not in the condition wherein it is exposed straight from the end surface of a front end portion of the lancet body when the lancet cap is removed from the lancet body upon pricking. When an injector ejects such lancet body toward a predetermined position, the front end portion of the pricking member is to stick in the predetermined position obliquely as to such portion (in spite of an intention that it essentially pricks at a right angle or an angle close thereto). In this case, the direction along which the lancet body moves is not corresponding to the direction along which the front end portion of the pricking member pricks the predetermined position.
As a result, since the front end portion of the pricking member tries to move obliquely in the skin, smoothly moving of that portion in the skin becomes more difficult compared with a case in which the pricking member is not curved (or flexed), so that pain which is felt upon pricking is increased. Therefore, it is desirable that curving (flexing) of the pricking member, particularly an area around the front end portion thereof is suppressed.
In order to suppress the above mentioned curving (or flexing) of the pricking member, a production process of a lancet is proposed in which an outer peripheral portion of a lancet cap is thicker while a portion of the lancet cap close to a front end portion of the pricking member is thinner (see Patent Document 1 below).
As to the lancet produced by the above mentioned process, a portion between the front end portion of the pricking member and the outer peripheral portion is thin. Thus, in a mold with which such lancet is formed, its passage for a molten resin to be injected through a point corresponding to a leading end of the lancet cap is narrow in an area corresponding to such thin portion. It is said that as a result, a velocity of the molten resin which passes through such narrow area is tentatively lowered, so that the inertia of the injected resin is equalized, whereby a force which intends to curve the front end portion of the pricking member is relaxed.
However, in order to produce the same number of the lancet as conventional according to the above mentioned process, an injection pressure of the molten resin should be increased because the passage for the molten resin is narrow. In this case, the inertia of the injected molten resin becomes larger, so that there comes a problem in that the effect of curving suppression may be insufficient. On the other hand, when the injection pressure of the molten resin is reduced, it takes a longer time to fill the mold with the molten resin, so that there comes a problem in that the same number of the lancet cannot be produced.
Patent Document 1:
Japanese Patent Kohyo Publication No. 2005-529704